The present invention relates generally to an automatic work guiding apparatus particularly for a sewing machine, and more particularly to such automatic work guiding apparatus wherein a rotary wheel engaging a work fabric to guide the same relative to a reference line during a sewing cycle is automatically adjusted in its pressure of guiding contact with the work fabric to an optimum level depending upon specific material, thickness, stiffness and other properties of the work fabric.
In the art of forming successive stitches along a predetermined seamline which is inwardly offset from the side edge contour of a workpiece such as a sheet or layer of fabric or other materials, there has been known an automatic workpiece guiding apparatus which comprises: a detecting device disposed ahead or in front of a stitch forming position or needle position in the direction of workpiece feeding and sensing a lateral deviation or displacement of the side edge of the workpiece from a predetermined reference position; a rotary wheel supported engageably with the workpiece and rotatably about an axis substantially parallel to the workpiece feeding direction; first drive means for rotating the rotary wheel to move the workpiece in the direction perpendicular to the workpiece feeding direction according to detection signals from the detecting device; and a contact pressure adjusting mechanism for adjusting as required a pressure of contact or engagement of the rotary wheel with the workpiece.
In such automatic workpiece guiding apparatus known in the art, however, it has been required to conduct, prior to a production sewing, a trial sewing operation each time the workpiece is changed from one kind to another. This trial sewing is performed with a contact pressure of the rotary wheel which is predetermined at a level which is supposed to be suitable to the new workpiece. Therefore, the trial sewing has to be repeated several times until an optimum contact pressure of the wheel has been established. Thus, the conventional workpiece guiding apparatus requires a long time and a high standard of skill of the operator for such trial sewing. For assuring fine stitching results, on the other hand, it is of prime importance to set up an optimum level of contact pressure of the wheel against the workpiece, in view of the fact that a lower contact pressure thereof than required will reduce the ability of the wheel to guide the workpiece and consequently cause a failure in forming the stitches at correct positions along the side edge of the workpiece, while a higher contact pressure thereof than required will cause sewing defects such as offsetting of some stitches away from the seamline and irregularity in pitch between the stitches due to strain or deformation of the workpiece under the excessive.